The Dogwhelk: A Study in Adaptation

Producer: Films for the Humanities and Sciences

We might expect shores that are exposed to considerable wave action to harbour marine life of a type different from that of a more sheltered shore. Using Nucella lapillus, a species of dogwhelk, these experiments compare substantial samples of dogwhelks taken from both locations. The two groups are compared for shell height and shape, body form, wet tissue weight, shell volume, and the amount of force required to remove it when attached. The dogwhelks are eaten by various predators, and a further experiment is carried out with the most important of these, certain littoral crabs. These crabs are present in far greater quantity at the sheltered than at the wave-swept site; the severity of the wave action and the lack of suitable refuge sites are probably responsible. In the experiment, the crabs are offered a choice of dogwhelks in different size ranges and with thin or thick shell lips. Some are eaten and others rejected. From what they have observed and data given in the guide, students will be able to make deductions about the relationships between location and shell shape and size.


Format: VHS NTSC
Running time: 15 mins.
Price: US$59.95